If chatter vibration which is a type of self-excited vibration occurs in a case where a workpiece is being worked by the rotation of a tool, the surface roughness and the external appearance of a worked surface are degraded, and thus hand finishing work is required for the degraded place. In addition, the working is, for example, cutting.
In the related art, as a method of suppressing such chatter vibration of a machine tool, there is a method of determining the number of rotations of a tool in which it is difficult for chatter vibration to occur, by finding a transfer function of a system in which chatter vibration occurs, which includes the tool or a workpiece, by an impulse response test, calculating convergence and divergence of the chatter vibration occurring during working in a range of a cut depth at the time of working or the number of rotations of the tool, and determining a stability limit line diagram.
Further, as stated in PTL 1, there is also a method of suppressing chatter vibration by performing working by using the number of rotations in which a chatter frequency during working of a system in which chatter vibration occurs is calculated by Equation (1) below, as a stable rotation speed.
                              [                      Equation            ⁢                                                                      ⁢                                                                    ⁢            1                    ]                ⁢                                                                                                Stable          ⁢                                          ⁢          rotation          ⁢                                          ⁢          speed                =                              fc            ×            60                                Z            ×            K                                              (        1        )            
In addition, fc is a chatter frequency, Z is the number of cutting teeth of a tool, and K is an integer.